fix: code contains spaces in headings (cotes2020#644)

(cherry picked from commit 3fa1bf3)

_includes/refactor-content.html

@@ -214,7 +214,7 @@
 
       {% assign left = snippet | split: mark_end | first %}
       {% assign right = snippet | slice: left.size, snippet.size %}
-      {% assign left = left | replace: '">', '"><span class="mr-2">' | append: '</span>' %}
+      {% assign left = left | replace_first: '">', '"><span class="mr-2">' | append: '</span>' %}
 
       {% assign _new_content = _new_content | append: mark_start
           | append: left | append: anchor | append: right